1. Field of the Invention
This invention relates to a novel process for upgrading heavy oils. The invention more particularly relates to an improved process for solvent deasphalting heavy oils and the production of gasoline and distillate boiling range hydrocarbons from the deasphalted oil.
2. Description of the Prior Art
It is now recognized that future energy needs will have to be satisfied at least in part by synthetic fuels production and from the upgrading of heavy petroleum feedstocks. The production of synthetic olefinic and/or aromatic high quality gasoline hydrocarbons from the catalytic conversion of various oxygenated organic compounds is well established. For example, U.S. Pat. No. 3,894,106 discloses a process for converting olefinic ethers to olefins and/or aromatics containing a greater number of carbon atoms by contacting the ether with a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12 and a constraint index of about 1 to 12 at elevated temperatures. The preferred catalysts are those of the ZSM-5 family. Similarly, U.S. Pat. No. 3,894,107 discloses the conversion of lower olefinic organic hetero compounds to olefinic and/or aromatic hydrocarbon compounds in the presence of ZSM-5 type of synthetic aluminosilicate molecular sieves.
U.S. Pat. No. 3,899,544 discloses the zeolite catalytic conversion of alcohols and/or ethers to gasoline boiling range hydrocarbons in which the zeolite catalyst contains about 30 to 85 percent of the total cation sites satisfied by a Lewis or Bronsted base such as elements of Group IA or VA of the Periodic Table. Particular exemplary cations disclosed include those which contain sodium, potassium, nitrogen and phosphorus, alone or in appropriate cationic complex form.
U.S. Pat. No. 3,928,483 discloses the production of gasoline boiling-range hydrocarbons from an alcohol or ether starting material. In accordance with the patent, C.sub.1 to C.sub.3 alcohols are converted to highly aromatic gasoline boiling-range hydrocarbons by first contacting an alcohol reactant with a condensation catalyst to produce water, heat and a predominately olefinic or organic intermediate product, and in a second stage contacting the intermediate product with a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least 12 and a constraint index of 1 to 12 to convert the intermediate product to a final gasoline product which may contain some water.
The above patents are but a few of the patents relating to the conversion of lower organic compounds containing heteroatoms, such as oxygen, sulfur and/or halogen, over a special class of crystalline zeolite catalysts at elevated temperatures to form hydrocarbons in the gasoline boiling range. The conversion is typically carried out at a temperature in the range of about 500.degree. to 1200.degree. F., preferably at a temperature in the range of about 600.degree. to 850.degree. F. and at space velocities in the range of about 0.5 to 50 LHSV. The product obtained comprises water, light hydrocarbon gases (C.sub.4.sup.-) and a normally liquid hydrocarbon fraction (C.sub.5.sup.+) which contains a substantial amount, usually at least about half, of C.sub.6 to C.sub.10 monocyclic aromatic hydrocarbons.
It has recently been discovered that low acidity zeolites, especially alkali metal ZSM-5, can catalytically upgrade heavy oils such as the residual fractions of crudes higher-boiling than 600.degree. F. to produce gasoline and distillate boiling-range hydrocarbons. U.S. Pat. No. 4,263,129 discloses converting high boiling hydrocarbon stocks to liquid products of lower boiling range over low acidity ZSM-5 type catalysts, such as NaZSM-5 at pressures ranging from at least 200 psig and temperatures ranging from 650.degree. to 850.degree. F.
Heavy oil feedstocks often contain large amounts of asphaltenes. Asphalt yields as high as 65 percent have been obtained from heavy crudes. Asphalts are undesirable in feeds to catalytic cracking processes because asphalts go largely to coke under process conditions. Deposition of coke on the cracking catalyst greatly reduces catalyst activity. Thus, it would be beneficial to separate the asphaltenes from the heavy oils before catalytic upgrading. Atmospheric distillation, acid treating, vacuum distillation, and solvent deasphalting have been used to separate asphalts from heavy oil feedstocks.
In solvent deasphalting processes, non-polar solvents (e.g., pentane, hexane or heptane) which have surface tensions less than 23 dynes/cm at 25.degree. C. have been used to precipitate asphaltenes from heavy oil feedstocks. A commercially important solvent deasphalting process uses liquid propane at 100.degree. to 210.degree. F. and 220 to 650 psig to extract a lubricating oil base stock and precipitate resins and asphalts from petroleum resid. After thermally separating the propane solvent from the deasphalted oil, the propane is condensed and recycled to the extraction tower. However, due to the large volumes of solvent required and to the high solvent recovery cost in liquid propane deasphalting, solvent deasphalting is not typically used as a processing step for upgrading heavy oils to gasoline and distillate. Thus, solvent deasphalting of heavy oils has been primarily limited to extracting lube oil base stock.